1. Field of the Invention
The present invention relates to a developing device for use in an electrostatic copying apparatus and more particularly, to a developing device of this kind which is so arranged that, by supplying mono-component magnetizable toner onto a developing sleeve which is driven for rotation, a magnetic brush is formed on the developing sleeve by the action of a stationary permanent magnet provided within the developing sleeve, while the bristle length of the magnetic brush is restricted by a bristle cutting member.
2. Description of the Prior Art
Conventionally, in a developing apparatus which is arranged to form a magnetic brush by supplying mono-component magnetizable toner onto the peripheral surface of a developing sleeve to be rotated around a stationary permanent magnet, the surplus mono-component magnetizable toner of the magnetic brush cut off by the bristle cutting member for restricting the bristle length tends to stay stationarily at the upstream side of the bristle cutting member with respect to the rotational direction of the developing sleeve, thereby to cause the mono-component magnetizable toner to be solidified. Thus, an undesirable blocking phenomenon is liable to take place. Upon occurrence of the blocking phenomenon as described above, the mono-component magnetizable toner is blocked by the solidified mono-component magnetizable toner and can not be transported up to the developing position, thus making it impossible to effect developing.
Meanwhile, the remaining mono-component magnetizable toner which has not been used for development at the developing position is continuously rotated as it is attracted onto the predetermined position of the developing sleeve, thereby to be magnetized by the powerful magnetizing action from the permanent magnet, with corresponding reduction of fluidity of the mono-component magnetizable toner. Accordingly, the state of brush bristles of the magnetic brush can be maintained constant, thus resulting in irregular development through reduction of developing efficiency.
Accordingly, an object of the invention is to provide an improved developing apparatus for use in an electrostatic copying apparatus which is capable of preventing the blocking phenomenon of the mono-component magnetizable toner by a bristle cutting member, and also capable of maintaining the proper fluidity of the mono-component magnetizable toner and also uniformity of formation of the brush bristles of the magnetic brush, through solution of the technical problems as described above.
In the prior art developing device which is arranged to form a magnetic brush by supplying developing material onto a developing roller for development by rubbing a photoreceptor against the magnetic brush, there have been such disadvantages that the developing material accommodated in the storage container is formed into lumps so as to cause the so-called blocking phenomenon. Thus, smooth supply of the developing material from the storage container to the developing roller is obstructed, consequently giving rise to faulty developments such as irregular developing, insufficient developing, etc. Especially, when the mono-component magnetizable toner is employed as the developing material, the undesirable blocking phenomenon tends to take place more easily, since particle diameters thereof are generally small, i.e. in the region of 5 to 30.mu.. For solving the technical problems as described above, there has conventionally been proposed an arrangement in which a stirring or agitating means to be driven by a main motor of the electrostatic copying apparatus is provided in the storage container. However, the known arrangement as described above also has a disadvantage in that the construction thereof is complicated.
Accordingly, another object of the invention is to provide an improved developing device capable of preventing the blocking of the developing material within the storage container, and also capable of supplying the developing material to the developing roller by approximately a predetermined amount through simple construction, with substantial elimination of the technical problems inherent in the prior art arrangements as described above.
The invention still further relates to a device for detecting the presence of a developing material in a developing device for use in an electrostatic copying apparatus, and more particularly to such a presence detection device for use in a developing device arranged to form a magnetic brush by supplying developing material onto the peripheral surface of a developing sleeve provided therein with a stationary permanent magnet and driven for rotation.
In a typical prior art device is arranged to effect detection by a light detector such as a photo-cell. But such a known arrangement has a disadvantage that such an optical detecting mechanism as described above is complicated in construction and generally expensive.
Accordingly, an another object of the invention is to provide an inexpensive presence detection device with simple construction for use in a developing device of an electrostatic copying apparatus.